energy & ecosystems

• how do plants use sugars from photosynthesis?

  1. respiratory substrates
  2. to synthesise other biological molecules - cellulose
• what is biomass?

  total dry mass of tissue or mass of carbon measured over a given time in a specific area
• suggest units for biomass?

  • area - gm-2
  • volume - cm-3
• how can chemical energy store in dry biomass be estimated?

  using calorimetry
• why is bomb calorimetry preferable to simple calorimetry?

  reduces heat loss to surroundings
• define gross primary production?

  total chemical energy store in plant biomass resulting from photosynthesis
• define net primary productivity?

  chemical energy store in plant biomass after respiratory losses to environment
• why is most of suns energy not converted to organic matter?

  1. solar energy absorbed by atmosphere/reflected by clouds
  2. photosynthetic pigments cannot absorb some wavelengths of light
  3. not all light falls directly onto chlorophyll
  4. energy lost at heat during respiration/photosynthesis
• why does biomass decrease along a food chain?

  1. some food not digested so passes out of body in faeces
  2. some lost due to excretion of metabolic waste products - urea
  3. some remains in uneaten parts - roots of plant, bones, teeth
  4. some used to create atp in respiration to allow organisms to carry out energy requiring movements
  5. some lost as heat
• define primary productivity?

  rate at which energy is converted to organic substances
• define secondary productivity?

  rate at which consumers convert chemical energy in their food into their biomass
• 2 ways farming practices increase efficiency of energy transfer?

  1. reducing respiratory losses to environment
  2. simplifying food webs
• reducing respiratory losses of livestock?

  1. kept in pens to restrict movement
  2. keep indoors where its warm so less energy wasted through releasing heat in respiration
  3. control feeding so animals receive optimum amount of food
  4. exclude predators
• simplifying food webs?

  1. chemical pesticides - less energy transferred to pests
  2. herbicides - to kill weeds which compete with crops for light energy
  3. biological agents - remove pests
• explain why length of food chains is limited?

  energy is lost at each trophic level so theres insufficient energy to support a higher trophic level
• what is a pyramid of biomass?

  diagram that shows the biomass at each trophic level
• why is a pyramid of biomass preferable to a pyramid of numbers?

  shape of pyramid of numbers may be skewed since small number of producers can support many consumers
• who are the producers in a food web in any ecosystem?

  plants
• why are plants producers in a food web?

  can create their own carbohydrates using carbon dioxide/water
• Describe the advantages and disadvantages of using chemical pesticides to control pests of crops?

  1. Acts quickly
  2. Can apply to particular area
  3. Kills all/most/wide variety of pests
  4. Needs to be re-applied
  5. Not specific
  6. Pests can develop resistance
  7. accumulation